DATA DROPPED FROM 2GB TO 1GB ON CONTRACT

I signed a 24 month contract through Autopage wiith vodacom and this contract includes 2GB free data. I have now seen that my data agreement has been changed to 1GB and my phone bill has gone from R1000 to R1900 in 2 weeks? This is unacceptable as my contract which I signed includes 2GB data. The contarct also includes fixed call rates. This needs to be fixed, this is ********* and not fair and I am owed data for the past month. i will cancel my debit order and will change service providers as I am due for cancellation of the contract on 26 May, if this is not sorted.